Der Spiegel said Merkel's mobile telephone had been listed by the NSA's Special Collection Service (SCS) since 2002 - marked as "GE Chancellor Merkel" - and was still on the list weeks before Obama visited Berlin in June.

In an SCS document cited by the magazine, the agency said it had a "not legally registered spying branch" in the US embassy in Berlin, the exposure of which would lead to "grave damage for the relations of the United States to another government".